1. Field of the Invention
The present invention relates to a ball valve that opens and closes a fluid communication passage or changes the direction of fluid flow by rotating a valve body installed in a housing about a given rotational axis, and more particularly to a ball valve that shuts off a fluid passage formed in a housing by rotating a valve body while keeping it out of contact or substantial contact with an annular seat member disposed on the peripheral edge of an inside open end of the fluid passage, and displacing the valve body towards the seat member while keeping a non-through opening portion of the valve body facing the seat member, thereby bringing the valve body into tight contact with the seal member.
2. Related Art
Hitherto, various types of valves for opening and closing a fluid passage for fluid communication or changing the fluid flow direction have been proposed. Among them, well known is a ball valve that has a ball-shaped valve body and a housing, in which the valve body is rotatable about a given rotational axis and has a communication hole that extends through the valve body along an imaginary surface orthogonal to the rotational axis, and the housing has the valve body installed therein and has at least two communication passages that communicate with each other via the communication hole of the valve body (for a two-way valve, two communication passages, namely an upstream-side communication passage and a downstream-side communication passage are provided, and for a three-way valve, three branched communication passages are provided).
The ball valve of the above type generally has an annular seat member that is to the peripheral edge of an inside open end (an open end located within the housing) of each communication passage in order to ensure the sealing against the valve body during the shut-off of the communication passage, and is structured to have the valve body rotated while being kept in contact (or sliding contact) with the seal member. This type of the ball valve poses a problem in that when the valve body is rotated or slidingly rotated while being kept in contact with the seat member continuously applying a surface pressure, the seat member is worn away and hence the sealing capability may not last for a long period of time.
In order to address the above problem, there is provided a two-way valve (a ball valve), as illustrated in FIG. 8, in which an annular seat member 101 is disposed on the peripheral edge of an inside open end of a communication passage A, one of fluid passages A, B that face each other via a valve body 100, the valve body 100 is rotated while being kept out of contact or kept out of substantial contact with (kept in slight contact with) the seat member 101 and then displaced towards the seat member 101, thereby allowing a non-through opening portion of the valve body 100 to be brought into tight contact with the seat member 101 thereby applying a surface pressure thereto and hence shutting off fluid flow between the fluid passages A, B (cf. Patent Document 1 for example).
The ball valve of the above type allows the non-through opening portion of the valve body 100 to be brought into tight contact with the seat member 101 by continuously rotating a shaft member 102 for rotating the valve body 100, thereby rotating the valve body 100, and then displacing the same towards the seat member 101.
Specifically, the ball valve has a projection 103 formed on a lower portion of the valve body 100 to extend along a given rotational axis L of the valve body 100, and the projection 103 is fitted into a recess 104 formed in a housing 108 so that the valve body 100 is supported in such a manner as to be rotatable about the given rotational axis L. The valve body 100 has a communication hole 106 that is formed by a straight through-hole for communication between the two communication passages A, B, and a communication hole 105 for receiving the shaft member 102, which is formed opposite to the projection 103 to communicate the communication hole 106 with the outside. Two pin members 107, each having an axis substantially parallel to the axis of the communication hole 106, are located inside the through-hole 105 with a given interval therebetween, and a shaft member 102 (or a transmission member 109 later described) is interposed between the pin members 107, 107.
The shaft member 102 extends into the housing 108 and the valve body 100 so as to be movable in the axial direction and rotatable about the axis. Specifically, the shaft member 102 has a first end formed with the transmission member 109 that is inserted between the pin members 107, a second end formed with an outwardly threaded portion 110 that projects outwards from the housing 108, and a guide groove 112 formed on an outer circumference (or a portion extending in the housing 108) of the shaft member 102 closer to the first end than the outwardly threaded portion 110 is, for receiving a guide pin 111.
An inwardly threaded member (or a nut member) that rotates upon receiving driving power from a driving source is threaded onto the outwardly threaded portion 110 of the shaft member 102 so that the shaft member 102 is moved forward and rearward in the axial direction upon driving the inwardly threaded member 113. The guide groove 112 is made up of a rotation guide portion 112a that is twisted in the circumferential direction as it advances from the first end towards the second end, of the shaft member 102, and a straight guide portion 112b that connects with the rotation guide portion 112a and extends straight towards the second end along the axis of the shaft member 102. As described above, the shaft member 102 is moved in the axial direction, so that the guide groove 112 (and hence the shaft member 102) is guided by the guide pin 111, the shaft member 102 is rotated 90° about the axis while being moved in the axial direction, and the non-through opening portion of the valve body 100 is moved straight in the axial direction while being kept facing the seat member 101.
The transmission portion 109 has parallel surfaces formed opposite to each other with the axis therebetween, and is made up of a rotation transmitting part 109a having the parallel surfaces interposed between the two pin members 107, 107 of the valve body 100, and a pressing-force transmitting part 109b having inclined surfaces continuously formed with the parallel surfaces. The transmission portion 109 is so structured that when the shaft member 102 has been rotated 90°, its rotational force is transmitted to the pin members 107 (and hence the valve body 100) via the parallel surfaces of the rotation transmitting part 109a, and as the shaft member 102 is moved forward subsequent to the rotation of the valve body 100, the inclined surfaces of the pressing-force transmitting part 109b are pressed against the pin members 107, thereby pressing the valve body 100 (more specifically the non-through opening portion) against the seat member 101.
Whereby, the ball valve having the above structure is capable of changing the communication passages A, B from an opening state to a closing state by rotating the shaft member 102, thereby rotating the valve body 100 while keeping the same out of contact or substantial contact with the seat member 101, and finally bringing the valve body 100 into tight contact with the seat member 101. The communication passages A, B can be changed from the closing state to the opening state by reversely rotating the shaft member 102, thereby moving the valve body 100 away from the seat member 101, and then rotating the valve body 100 while keeping the same out of contact or substantial contact with the seat member 101.
(Patent Document 1) U.S. Pat. No. 3,515,371
The ball valve having the above structure, which opens and closes the communication passages A, B by moving forward and rearward in the axial direction the shaft member 101 extending in the valve body 100 and the housing 108, poses a problem in that increase of an area, through which the shaft member 101 is moved forward and rearward, results in increase of an installation space of the ball valve.
In addition, the ball valve having the above structure, in which the shaft member 102 is moved forward and rearward by rotating the inwardly threaded member 113 relative to the outwardly threaded portion 110 formed on the shaft member 102, poses a problem in that it takes a time to achieve the axial movement of the shaft member 102, and hence it is difficult to open and close the communication passages in a short time.
As an additional problem associated with the ball valve having the above structure, since the communication passages A, B are opened and closed by drivingly rotating the inwardly threaded member 113, which is threaded onto the shaft member 102, thereby moving the shaft member 102 forward and rearward in the axial direction, it takes a time to open and close the communication passages A, B, as described above, it is very difficult to adjust the opening degree of each of the communication passages A, B, and complicated settings are required for automatic flow-rate control or the like.
In consideration of the above problems, it is an object of the present invention to provide a ball valve having a reduced size, which is capable of easily and instantly opening and closing communication passages, and changing the direction of fluid flow, while being capable of minimizing the wearing of a seat member for shutting off a fluid passage, by having a valve body rotatable while being kept out of contact or substantial contact with the seat member.